整合求解器活动监控与步长回归证据

同步远端 PNL0003 诊断和大采样网格能力，语义合并活动感知的 60 秒真停滞判定与旧后端 15 分钟兼容兜底。

纳管热路径优化、15 单元运行证据、浏览器与 API 报告，并补充北京时间更新日志和遗留问题。

app/simulation/components/amesim/junctions/nodes.py

@@ -163,6 +163,9 @@ class AmesimPn3Node2(_AmesimPneumaticNode):
     MODEL_TYPE = "amesim_pn3node2"
     MODEL_VERSION = "0.3.0"
     PRESSURE_FLOW_DEPENDS_ON_STREAM = False
+    PRESSURE_FLOW_EXACT_SUM_TO_ZERO_EQUATION_SUFFIXES = frozenset(
+        ("mass_flow_balance",)
+    )
     PORTS = (
         PortDefinition.pneumatic("port_1", nominal_role="bidirectional"),
         PortDefinition.pneumatic("port_2", nominal_role="bidirectional"),
@@ -200,6 +203,9 @@ class AmesimP4Node2(_AmesimPneumaticNode):
     MODEL_TYPE = "amesim_p4node2"
     MODEL_VERSION = "0.3.0"
     PRESSURE_FLOW_DEPENDS_ON_STREAM = False
+    PRESSURE_FLOW_EXACT_SUM_TO_ZERO_EQUATION_SUFFIXES = frozenset(
+        ("mass_flow_balance",)
+    )
     PORTS = (
         PortDefinition.pneumatic("port_1", nominal_role="bidirectional"),
         PortDefinition.pneumatic("port_2", nominal_role="bidirectional"),